US 2006/0020597 is concerned with making use of visual image content evaluation to effect a variety of interactions with visual images, such as, for example, indexing of a collection of visual images, grouping of visual images of a collection of visual images, summarization of a collection of visual images, annotation of groups of visual images, searching for visual images and identification of a representative visual image from a group of visual images. Groups of visual images in a collection of visual images can be annotated by identifying an image representation for each of the groups, determining the similarity of each of the image representations to each of the other image representations, and annotating the groups of visual images based on the similarity of each image representation to the other image representations. The image representation for a group of visual images can be an average of one or more image characteristics for all visual images of the group of visual images.
A problem of the known method is that the average value of an image characteristic is often not meaningful. In particular for large groups of images, the average value of the image characteristic will tend to be the median value of the range of possible values of the characteristic. This makes the annotation less suitable for browsing and searching hierarchically organized visual images.